I think its about 4 meters high - some guys park a small bus there and the top is the right height for a good track view.
The problem with the MB campsite is the the trackside front portion is limited to a very thin strip except where you suggested going (the bank is in front of you) or where Beermountain goes higher up. Higher up the problem is that they don't put up the safety fence until around Wed/Thu, so you could have to remove the tower altogether...sorry not to sound more positive, but I get the impression you have a big set up so should know.
If you used to camp opposite us in KN campsite - did you not have a 2/3 level tower with a bar at the bottom? - if this was you it would be a good height to go where you are planning!
Hope that helps. If you take our spot can I come and watch from your tower?!
Mr T, Bog Triangle Residents Association, MB Campsite